1. Field of the Invention
The present invention relates to retroreflective sheeting having a printed layer useful for signs such as road signs and construction signs; license plates of automobiles, motorcycles, etc.; safety garments and lifesaving equipment; sporting goods such as snow poles; and marking materials such as commercial signboards. In particular, it relates to retroreflective sheeting having a printed layer which hardly ices over or holds snow on its surface in a cold district and, when stained with paint, ink, etc., can be cleaned simply by dry wiping or washing with water without using an organic solvent.
2. Description of the Related Art
A retroreflective sheet which reflects incident light toward the light source is well known, and its excellent visibility owing to the reflection performance has been taken advantage of in various fields as noted above.
However, the state-of-the-art retroreflective sheeting often has problems of reduction in visibility or retroreflective properties when used in cold districts. When temperature drops below 0° C. in winter, water drops adhering to a retroreflective sheet freeze to reduce the retroreflective properties. When it snows, snow tends to adhere to the retroreflective sheet, sometimes completely ruining the display function of the retroreflective sheet.
There is another problem recently encountered that the surface of signs, particularly road signs and construction signs, is intentionally spoiled by marking with paint, ink or another substance out of mischief.
In the light of these problems, the inventors of the present invention previously proposed retroreflective sheeting comprising a base retroreflective sheet having a flat front face layer on the light incident side and a fluorine-containing resin film having a total light transmittance of at least 80% provided on the flat front face layer via an adhesive layer (WO97/22098 and U.S. Pat. No. 6,110,574). The proposed retroreflective sheeting has resistance against icing and snow sticking, which is provided by a simple operation, and, when stained with paint, ink, etc., can be cleaned simply by dry wiping or washing with water without using an organic solvent that may adversely affect human bodies and the environment.
The retroreflective sheet of the U.S. patent has solved the problems discussed above but does not have a printed layer for displays or decoration. Because a fluorine-containing resin film generally has poor adhesion to a printed layer, if a printed layer is provided between the fluorine-containing resin film and the adhesive layer, water, a solvent, etc. may penetrate into the interface between the resin film and the printed layer to cause lifting, which can cause separation of the resin film.